active exaust?

[moonmonkey]

i have seen a 2cyl engine with an active port size (valve), that was added to lend low end torque to the engine while still allowing top end power. and we know that exaust size works better/worse depending on rpm and other factors, would an active exaust size ("valve") that was controlled by engine rpm,load and other fators help? i almost never exceed 3300 rpm and the majority of the time stay between2500-2750 rpm, since my engine hits peak torque at a higher rpm, could it be retuned to be more efficent at a lower rpm ? im talking about exaust pipe size not the valve in the head.

[drmiller100]

I've thought about doing that as a way to get a cheap man's variable valve timing. "Plug" the exhaust and get internal EGR, sort of, to reduce pumping losses.

Haven't tried it yet though.

[Ryland]

Yes, it should work, Toyota did something like that, only with their intake that worked well.

[Ladogaboy]

My car has that standard (MIVEC), but as far as I know, a lot of engineering went into making it work. You'd need customized cams and the engine would need to be tuned to maximize its benefits. Some research into how Mitsubishi's MIVEC exhaust works might yield some good information on where to focus and what, exactly, this modification would entail.